A delta motor system typically includes a delta motor, a three phase power source, a fault contactor and a motor controller. During start up, delta motors often experience potentially damaging high inrush currents and starting torques. This can adversely effect the performance of the motor drive and increase general wear and tear leading to higher maintenance costs. In addition, current peaks during motor startup can also cause voltage disturbances in the power supply.
Motor controllers are typically used to restrict the motor torque and reduce the high starting currents by controlling the application of voltage from the three phase power source to the delta motor. The motor controller generally includes a set of three control switches that are connected between the line voltage terminals of the three phase power source and the windings of the delta motor. The motor controller regulates the voltage from the three phase power source to the delta motor by selectively opening and closing the three control switches. The proper operation of the delta motor is dependent on the proper regulation of the control switches.
The fault contactor is commonly used to disconnect the three phase power source from the delta motor in the event that the delta motor system malfunctions. The fault contactor includes a set of three contacts that are also connected between each of the delta motor windings and the line voltage terminals. Each of the delta motor windings are adapted to receive the fault contact connection on one side and the control switch connection on the other side. Alternatively, the fault contactor function can be performed by a shunt trip circuit breaker, in-line contactor, or fuses.
The motor controller's internal timing mechanisms are specifically designed to regulate the application of specific line voltages from the three phase power source to specific delta motor windings based on a predesignated wiring configuration. Conventional electrical leads are typically used to connect the delta motor windings to the control switches and to the fault contacts. Since the electrical leads providing connection to the delta motor terminals are not always clearly marked, mistakes in wiring the delta motor system are common.
A common wiring error occurs when the delta motor terminals designated for connection to the motor controller control switches are connected to the fault contacts and the motor terminals designated for connection to the fault contacts are connected to the control switches. In this wiring configuration, the phase shift in the currents through each of the windings are no longer compatible with motor controller's internal mechanisms and although the delta motor will run, the motor controller will be unable to perform its necessary current limiting functions during start up or will be unable to supply full voltage to the motor for operation after starting.
Clearly it would be desirable to use a motor controller that automatically detects a fault condition when the fault contactor connections and the motor controller connections to a delta motor's windings have been swapped prior to actually running the delta motor 14. This will enable the user to correct the wiring error before starting the delta motor and subjecting it to potentially damaging overcurrent and increased torque conditions which can adversely effect the performance of the motor drive and increase general wear and tear leading to higher maintenance costs. The present invention seeks to achieve these objectives.